Treatment of hydrocarbons

ABSTRACT

Method and apparatus are described whereby a caustic-treated hydrocarbon feed mixture having a contaminating concentration of water and sulfur compounds is treated by separating the hydrocarbon feed into a first stream and a second stream. The first stream is contacted with an adsorbent material to produce a reactor feed stream having a significant reduction in the concentration of the contaminating water and sulfur compounds. The reactor feed stream is thereafter contacted in the presence of hydrogen under suitable isomerization conditions with an isomerization catalyst to produce an isomerate product.

This is a division of application Ser. No. 7/597,932, filed Oct. 15,1990, now U.S. Pat. No. 5,082,987.

This invention relates to the treatment of hydrocarbon-containingfeedstreams. The invention further relates to the removal of water andsulfur compounds from a hydrocarbon-containing feedstream prior toisomerization of said hydrocarbon-containing feedstream so as to improvereaction activity of the isomerization catalyst and conversion of thenormal hydrocarbons within the hydrocarbon-containing feedstream totheir corresponding isomers.

BACKGROUND OF THE INVENTION

The isomerization of paraffinic hydrocarbons having from 4 to 6 carbonatoms is practiced to create more highly branched isomers from thenormal or straight-chain hydrocarbons. One purpose of an isomerizationprocess is to provide high octane blend components for refined gasoline.The isomers can also be used in the production of other products or usedas solvents. For the isomerization of normal butane, it is generallydesired to produce an isobutane product that can be used as a feedstockin the manufacture of methyl tertiary butyl ether (MTBE) or in themanufacture of an alkylate product produced by the alkylation ofisobutane with olefin hydrocarbon compounds. The isomerization ofpentane, hexane, and refinery light naphtha mixtures is also practicedin order to produce high octane gasoline blending components. Theisomerication of normal or straight-chain hydrocarbons can significantlyimprove the overall octane number of the gasoline pool produced frompetroleum refining operations.

In the isomerization of paraffin hydrocarbons, it is desirable toisomerize a hydrocarbon-containing feedstream that contains a minimumamount of sulfur compounds and water because of their contaminatingeffects upon the isomerization catalyst. Generally, water serves as apoison to isomerization catalysts, and sulfur compounds act as temporarypoisons that inhibit catalyst isomerization activity. The larger theconcentration of water and sulfur compounds within ahydrocarbon-containing stream, the lower the attainable conversion perpass of the normal hydrocarbons to their corresponding isomer compounds,consequently resulting in lower product yields.

Recent developments in the process for producing linear low densitypolyethylene have resulted in the requirement that an extremely highpurity, essentially contaminant-free isopentane product be utilized as asolvent. Generally, this high purity isopentane requires that its sulfurcontent be less than 1 part per million by weight (ppmw) and that thewater content be less than 10 ppmw. Because of the more rigorous productspecification for isopentane that is to be used in the production oflinear low density polyethylene, it becomes more difficult and morecostly to produce. While there are a number of commercial processeswhich can be used for the production of this high purity product, manyof them are costly to operate and involve high initial capital costs.

There are many methods known in the art for removing water and sulfurcompounds from hydrocarbon-containing feedstreams. One such processinvolves the caustic treating of a hydrocarbon stream to remove sulfurcompounds as is described in U.S. Pat. No. 4,562,300 and the referencescited therein. One difficulty with the caustic treating method referredto above is that disulfide compounds are produced which have a slightsolubility in the hydrocarbon-containing stream being treated and,because of this slight solubility, small quantities of disulfidecompounds remain in the treated hydrocarbon-containing stream. Due tothe slight concentration of disulfide compounds in the treatedhydrocarbon-containing stream when it is charged to an isomerizationreaction zone, the isomerization catalyst activity is inhibitedresulting in a lower conversion and lower product yield. Therefore, theremoval of the small quantities of contaminating sulfur compounds fromthe hydrocarbon-containing feedstream prior to charging the feedstreamto an isomerization reaction zone can substantially improve catalystactivity and conversion. Additionally, the removal of the disulfidecompounds from the treated hydrocarbon-containing stream prior tocharging the stream to an isomerization reactor can result in providinga high purity isomerate that contains minimal quantities of sulfurcompounds.

It is, therefore, an object of this invention to provide an improvedmethod and apparatus for removing contaminating quantities of water andsulfur compounds from hydrocarbon-containing streams.

A further object of this invention is to provide method and apparatusfor enhancing the activity of isomerization catalyst in order to improvethe conversion of straight-chain hydrocarbons to their correspondingbranched chain isomers and to increase product yield.

A still further object of this invention is to provide method andapparatus for producing at low cost a treated hydrocarbon-containingstream suitable for isomerization.

Another object of this invention is to provide a method for producing anessentially contaminant-free, high purity isomerate product suitable foruse in the production of linear low density polyethylene.

SUMMARY OF THE INVENTION

Thus, the method of the present invention relates to treating acaustic-treated hydrocarbon feed mixture having a contaminatingconcentration of water and sulfur compounds by separating thecaustic-treated hydrocarbon feed mixture into a first stream comprisingnormal pentane and heavier hydrocarbon compounds and a second streamcomprising isopentane and lighter hydrocarbon compounds. The firststream is contacted with a molecular sieve material to adsorb water andsulfur compounds from the first stream and thereby produce a reactorfeed stream having a significant reduction in the concentration of waterand sulfur compounds contained therein. The reactor feed stream isthereafter contacted in the presence of hydrogen under suitableisomerization conditions with an isomerization catalyst to produce anisomerate product stream.

Another aspect of the present invention includes apparatus for treatinga caustic-treated hydrocarbon feed mixture having a contaminatingconcentration of water and sulfur compounds comprising first separatingmeans for separating the caustic-treated hydrocarbon feed mixture into afirst stream comprising normal pentane and heavier hydrocarbon compoundsand a second stream comprising isopentane and ligher hydrocarboncomounds. A significant reduction in the concentration of water andsulfur compounds in the first stream is achieved by contacting means forcontacting said first stream with a molecular sieve material to producea reactor feed stream. An isomerate stream is produced by utilizingisomerizing means for isomerizing the reactor feed stream by contactingsaid reactor feed stream in the presence of hydrogen under suitableisomerization conditions with an isomerization catalyst.

BRIEF DESCRIPTION OF THE DRAWING

Other aspects, objects and advantages of this invention will becomeapparent from the study of this disclosure, appended claims, and thedrawing in which:

FIG. 1 is a schematic representation of a process for treating andisomerizing a hydrocarbon feed mixture that includes the features of thenovel invention.

DETAILED DESCRIPTION OF THE INVENTION

Processes for the isomerization of normal hydrocarbons to theircorresponding branched compounds or isomers are generallyequilibrium-type processes in which the amount of conversion of normalparaffins to branched structures are limited by thermodynamicequilibrium factors. In most isomerization processes, it is desirablefor the isomerization reactions to take place at the lowest achievabletemperatures because the conversion of normal paraffins to theircorresponding branched structures generally increases as the reactiontemperatures are decreased. To achieve greater conversion of normalparaffins to their corresponding isomers, high activity isomerizationcatalysts are used which improve the reaction rate of isomerizationreactions at low reaction temperatures. One difficulty encountered withthe use of isomerization catalysts is that they are usually verysensitive to the presence of water and sulfur compounds. Generally, thepresence of water in the reactor feed and the presence of sulfurcompounds in the reactor feed work as poisons to the catalyst therebyinhibiting isomerization catalyst activity. The presence of thesecontaminants has the effect of lowering the attainable conversion of thenormal paraffins to their branched isomers and decreasing product yield.While sulfur compounds are often temporary poisons to the catalyst, itis still desirable to minimize the amount of sulfur compounds containedin an isomerization reactor feed material because of the improvement inconversion and yield that are achievable by lowering the concentrationof sulfur.

The inventive process utilizes a caustic treating step to remove asignificant presence of mercaptan type sulfur compounds from ahydrocarbon feedstream prior to isomerization and to convert remainingsulfur compounds to mainly disulfides, which can be separated from thehydrocarbon feedstream by simple separation methods such as byfractionation. Prior to caustic treating of the hydrocarbon feedstream,a hydrocarbon feed mixture from which the feed material forisomerization is taken passes through a separation step whereby theparaffin hydrocarbons desired for isomerization are separated as anoverhead stream from other hydrocarbons that are not desirable forisomerization, which are recovered as a bottoms product stream.

Any suitable hydrocarbon feed mixture can be utilized in this invention.Such suitable hydrocarbon feed mixtures can include hydrocarbondistillates, gasoline, which includes cracked gasoline, straight-rungasoline or mixtures thereof, naphtha, jet fuel, kerosene, andhydrocarbons having at least 4 carbon atoms. The preferred hydrocarbonfeed mixture is a hydrocarbon stream containing hydrocarbons having atleast 4 carbon atoms, but most preferred, the hydrocarbon stream shouldcomprise a pentane mixture.

In order to maintain a high isomerization catalyst activity, it isdesirable that there be no sulfur compounds contained within thehydrocarbon feed mixture. The inventive features of this invention havebeen developed for the purpose of removing at least a significantportion of the sulfur compounds contained within the hydrocarbon feedmixture prior to charging a particular portion of the hydrocarbon feedmixture to an isomerization reaction zone. Generally, the hydrocarbonfeed mixture will be a sour hydrocarbon stream containing significantquantities of sulfur compounds with the concentration of such compoundsranging upwardly to about 2 weight percent, or more. While the type ofsulfur compounds can vary significantly, the compounds that aregenerally present are mercaptans, sulfides, disulfides, and thiophenes.

Prior to the treating of a hydrocarbon feed mixture stream to remove asignificant portion of the contaminating sulfur compounds containedtherein, the hydrocarbon feed mixture stream can optionally undergo aseparation step. In this separation step, the lighter hydrocarbons,which are the more preferred isomerization feed materials, are separatedfrom the heavier hydrocarbons. It is generally preferred to separatehydrocarbons having less than 7 carbon atoms from those hydrocarbonshaving more than 6 carbon atoms. The most preferred split of thehydrocarbon feed mixture stream is to separate the hydrocarbons havingless than 6 carbon atoms from those hydrocarbons having more than 5carbon atoms.

Any suitable means for separating the hydrocarbons can be used. Many ofthe various separating means known in the art are disclosed at length inPerry's Chemical Engineers' Handbook, (6th edition, 1984) and caninclude conventional distillation methods, liquid-liquid extractionmethods, adsorption processes, and such novel processes as those thatuse permeable membranes for separation. The preferred separation means,however, is the use of conventional distillation methods. The separatedhydrocarbon stream, which consists essentially of hydrocarbons havingless than 7 carbon atoms, or preferably less than 6 carbon atoms, is fedto caustic treating means for the removal of sulfur compounds to producea caustic-treated hydrocarbon feed mixture. There are many known andsuitable methods for caustic treating hydrocarbon streams for thepurpose of removing contaminating levels of sulfur compounds. One suchsuitable method comprises contacting a hydrocarbon stream with analkaline solution that comprises water and an alkaline reagent. Thesolution can be regenerated by a catalyzed reaction of sulfur compounds,which generally are organic sulfur compounds such as mercaptans, todisulfides and a subsequent separation of the thus formed disulfidesfrom the solution. For reference, suitable caustic treating means arethoroughly described in U.S. Pat. No. 4,562,300 and in the referencescited therein.

The alkaline solution composition generally is an aqueous solution withthe alkaline present in the range generally from about 5 to about 50weight percent, but preferably in the range of from about 10 to about 15weight percent. The preferred caustic material is an aqueous solution ofsodium hydroxide in water. Other materials such as potassium hydroxideand lithium hydroxide in aqueous solution can be used.

The alkaline solution is contacted with the hydrocarbon feedstream in acountercurrent extractor. This extraction process takes place attemperatures in the range of from about 100° F. to about 150° F. andpressures in the range of from about 60 psig to about 110 psig.Preferably, the temperature in the contactor or extractor will be about125° F., and the pressure will be about 85 psig. The weight ratio offeed to alkaline solution fed into the extractor should range from about2.0 to about 4.0. In the contactor, mercaptans such as methyl mercaptanand isopropyl mercaptan are removed to form RSNa and water where R is analkyl group.

The contacting apparatus can be chosen from any common contactingapparatus, but it is preferably a countercurrent liquid-liquid trayedcontactor. This apparatus preferably contains perforated trays. Thealkaline solution can flow, for example, from the top to the bottom ofthe apparatus countercurrently to the hydrocarbon feed. The treatedhydrocarbon feedstream leaves the extractor and can be further treatedand separated through conventional means.

The contacted alkaline solution exits from the extractor and is theninjected into an oxygenation reactor. In the oxygenation reactor, themercaptans are oxygenated to disulfides. A catalyst can also be used inthe oxygenation reactor. The thus formed organic disulfides areinsoluble in the aqueous alkaline solution. Some of the sulfur materialswill remain unreacted from the oxygenation reactor. This stream is thensent to a settler to separate the disulfides from the alkaline stream.

The mercaptan rich alkaline solution is heated to the temperature rangeof from about 145° F. to about 150° F. prior to feeding the solution tothe oxygenation reactor. Air is injected and the flow is cocurrent inthe oxygenation reactor, which can be any conventional reactor, butpreferably is a packed column containing one inch diameter Raschigrings. The pressure in the oxygenation reactor will range from about 70to about 75 psig.

After the oxygenation step, the alkaline and sulfur material are passedto a phase separator where alkaline solution containing upwardly toabout 60 ppmw, or more, total organic sulfides and disulfides areseparated from an organic disulfide phase.

In most instances, the above-described caustic treating means providesan effective removal of the organic sulfur compounds that are containedwithin hydrocarbon feed mixture streams; however, because of thesolubility of disulfide compounds in hydrocarbon mixtures and because ofthe less than complete removal of sulfur compounds from a hydrocarbonfeed mixture, the caustic-treated hydrocarbon feed mixture can contain aconcentration of sulfur compounds. Furthermore, because the contactingsolution utilized in caustic treating means is an aqueous solution, thecaustic-treated hydrocarbon feed mixture will be saturated with waterand potentially will have quantities of free water suspended therein.The sulfur concentration can range upwardly to about 150 ppmw and thewater concentration can range upwardly to about 200 ppmw. Generally, thesulfur concentration in the caustic-treated hydrocarbon feed mixturestream will range from about 40 ppmw to about 150 ppmw and the waterconcentration will range from about 100 ppmw to about 200 ppmw.

The caustic-treated hydrocarbon feed mixture can optionally be separatedinto a first stream and a second stream prior to contacting of at leasta portion of the caustic-treated hydrocarbon feed mixture with anadsorbent material to produce a product stream having a significantreduction in the concentration of the water and sulfur compoundscontained therein. The separating means can be any suitable means forsplitting the caustic-treated hydrocarbon feed mixture stream into afirst stream and a second stream, but it is preferable that conventionaldistillation means be utilized as a part of this invention. It ispreferred that the first stream from separating means comprise thatportion of the caustic-treated hydrocarbon feed mixture comprisingnormal alkane hydrocarbons having at least 4 carbon atoms. In the morepreferred embodiment of this invention, the caustic-treated hydrocarbonfeed mixture will comprise primarily normal pentane and isopentane, andseparating means will separate or split the normal pentane andisopentane into the two streams with the first stream comprisingessentially that portion of the caustic-treated hydrocarbon feed mixturethat is normal pentane and with the second stream comprising essentiallythat portion of the caustic-treated hydrocarbon feed mixture that isisopentane. The sulfur compounds and water contained within thecaustic-treated hydrocarbon feed mixture will concentrate essentially inthe first stream.

The first stream is contacted by contacting means with an absorbentmaterial used for removing the sulfur compounds and water present in thefirst stream. Any suitable adsorbent can be used, but the preferredadsorbent is a molecular sieve material of the crystalline form having auniform pore diameter of less than about 10 angstroms (Å). Suitablemolecular sieve materials are described in the art and includecommercially available molecular sieves such as Zeolite A, X, L, Y,mordenite, montmorillonite, baroid clays, and the like. Other suitableadsorbents may include supported nickel and molybdenum oxide and zincoxide. The preferred molecular sieve material for use in this inventionand for removing the water and sulfur compounds from the first stream isthe material known in the trade as type 13X. A type 13X molecular sieveis generally effective for adsorbing molecules having diameters of lessthan 10 Å and excluding molecules having diameters of greater than 10 Å.The type 13X molecular sieve material will have a nominal pore diameterof about 10 Å and will come in a form having a bulk density in the rangeof from about 25 to about 45 pounds per cubic foot.

It is generally desirable that by contacting the first stream with anadsorbent material, a significant reduction in the amount of sulfurcompounds and water contained within the first stream is achieved toproduce a suitable isomerization reactor feed stream or reactor feedstream. Preferably, the amount of sulfur compounds and water adsorbed bythe adsorbent material will be such that the concentration of sulfurcompounds in the reactor feed stream is less than 1 ppmw and theconcentration of water in the reactor feed stream is less than 10 ppmw.However, the concentration of sulfur compounds contained in the reactorfeed stream can range upwardly to about 150 ppmw and the concentrationof water in the reactor feed stream can range upwardly to about 200ppmw.

The reactor feed stream, having a significant reduction in theconcentration of the water and sulfur compounds, is fed to anisomerization reaction zone wherein the reactor feed stream is contactedin the presence of hydrogen under suitable isomerization conditions withan isomerization catalyst to produce an isomerication reactor product orreactor effluent or isomerate stream.

The isomerization of normal alkane hydrocarbons is generallyaccomplished in the vapor phase at reaction conditions including atemperature in the range of from about 300° F. to about 800° F. andpreferably in the range of from 475° F. to 575° F. The pressure in thereaction zone is generally in the range of from about 300 psig to about900 psig and preferably in the range of from 300 psig to 500 psig. Thehourly space velocity will fairly depend upon the operating temperatureand pressure and preferably will be in the range of from about 0.1hour⁻¹ to about 10 hours⁻¹, and more preferably, from about 0.5 hour⁻¹to about 5 hours⁻¹. The term "hourly space velocity" refers to thenumber of reactor volumes of feed at standard conditions of oneatmosphere and 60° F. which is treated per hour. The values for hourlyspace velocity are determined by the ratio of volumetric flow rate atstandard conditions and in terms of hours to the reactor volume.

The isomerization of the normal alkanes is performed in the presence ofhydrogen. Hydrogen is generally present in an amount of from about 0.1to about 10 moles of hydrogen per mole of feed, and preferably from 0.5to 5 moles of hydrogen per mole of feed. The presence of hydrogenfavorably improves the conversion of n-butane and n-pentane to isobutaneand isopentane, respectively. Furthermore, the presence of hydrogen inthe reaction zone helps reduce the formation of coke which tends topoison the isomerization catalyst. The hydrogen is recovered from theeffluent from the isomerization reactor and preferably purified andrecycled to the reaction zone. The hydrogen to the reaction zone maythus consist solely of recycle hydrogen or a mixture of recycle hydrogenand make-up hydrogen or, simply, make-up hydrogen. Generally, however, arecycle stream is used in the isomerization process.

Best isomerization results are obtained with the use of substantiallypure n-butane or n-pentane or mixtures thereof. Thus, preferably thefeeds will be at least 90 volume percent n-butane or n-pentane ormixtures thereof. However, the isomerization process can also beconducted with feeds, which, besides the n-butane or n-pentanehydrocarbons, or mixtures thereof, contain certain amounts of otherhydrocarbons. While the admixture of large percentages of heavierhydrocarbons, such as naphtha, has a damaging effect on the process orcause reactions which inhibit or suppress the isomerization of then-butane or n-pentane, or mixtures thereof, it is possible to have smallpercentages of such higher hydrocarbons with n-butane or n-pentane, ormixtures thereof.

The isomerization catalyst used in this invention can be any suitablecatalyst composition that provides for the equilibrium isomerization ofnormal alkane hydrocarbons. Examples of such suitable isomerizationcatalyst compositions are described in J. J. McKetta and W. A.Cunningham, Encyclopedia of Chemical Processing and Design, volume 27,pages 444-447, Marcel-Dekker, Inc., 1988. A preferred isomerizationcatalyst comprises a platinum group component in association with aporous solid carrier.

The porous solid carrier is a porous inorganic oxide and preferably ahigh surface area inorganic oxide, for example, an inorganic oxidehaving a surface area of from about 50 to about 700 m² /gm andpreferably from 100 to 700 m² /gm. Satisfactory porous solid carriersfor the preparation of the catalyst for use in the process of theinvention include silica, zirconia, magnesia, thoria, alumina, and thelike, and combinations thereof, for example, silica-alumina,silica-zirconia, alumina-silica-magnesia, alumina-thoria,alumina-thoria-zirconia, and the like.

Alumina is a particularly suitable carrier or support for the catalystused in the present invention. Furthermore, alumina can be prepared by avariety of methods for purposes of this invention. Thus, the alumina canbe prepared by adding a suitable alkaline agent such as ammoniumhydroxide to a salt of aluminum, such as, aluminum chloride, aluminumnitrate, and the like, in an amount to form aluminum hydroxide that upondrying and calcining is converted to alumina. Alumina may also beprepared by the reaction of sodium aluminate with a suitable reagent tocause precipitation thereof with the resulting formation of aluminumhydroxide gel. Also, alumina may be prepared by the reaction of metallicaluminum with hydrochloric acid, acetic acid, and the like, in order toform a hydrosol which can be gelled with a suitable precipitating agent,such as, ammonium hydroxide, followed by drying and calcination.

The most preferred carriers for the support of the platinum groupcatalyst are molecular sieve materials as previously described herein.

The platinum group component catalyst should contain a platinum groupcomponent in an amount of from about 0.01 to about 3 weight percent andpreferably in an amount from 0.1 to 1 weight percent based on thefinished catalyst. The platinum group component embraces all the membersof Group VIII of the Periodic Table having an atomic weight greater than100 as well as compounds and mixtures of any of these. Thus, theplatinum group components are the Group VIII noble metals or compoundsthereof. Platinum is preferred because of its better performance inisomerization reactions. Regardless of the form in which the platinumgroup component exists on the catalyst, whether as metal or compound,the weight percent is calculated as the metal.

The platinum group component is associated with the porous solid carrierby various methods. The platinum group component can be disposed on thecarrier by a suitable technique such as ion-exchange, impregnation,coprecipitation, and other similar methods. Generally, it is preferredthat the platinum group component be associated with the porous solidcarrier by impregnation. The impregnation is generally accomplished withan aqueous solution of a decomposable compound of a platinum group metalin sufficient concentration to provide the desired quantity of theplatinum group component on the finished catalyst. Preferred platinumgroup decomposable compounds include chloroplatinic acid, ammoniumchloroplatinates, polyammineplatinum salts, palladium chloride, iridiumchloride, chloroiridic acid, and the like.

Various promoters can optionally be incorporated with the platinum groupcomponents to increase the activity, stability, and othercharacteristics of the catalyst. Metal promoters as, for example,rhenium, may be added. Also, combinations of one platinum groupcomponent with another platinum group component, such as, for example,platinum and iridium, can be used.

Halides, particularly fluoride or chloride, may be used to promote thecatalyst for isomerization of n-butane and/or n-pentane. Chloride is thepreferred halide. The halides apparently provide a limited amount ofacidity to the catalyst which is beneficial to most isomerizationreactions. A catalyst promoted with halide preferably contains fromabout 0.1 to about 10 weight percent, more preferably 3 to 6 weightpercent. The halide can be incorporated onto the catalyst at anysuitable stage of catalyst manufacture, for example, prior to orfollowing incorporation of the platinum group component. Some halide isoften incorporated with the catalyst by impregnation with the platinumgroup component; that is, for example, impregnation with chloroplatinicacid normally results in chloride addition to the catalyst. Additionalhalide may also be incorporated with the catalyst, if desired. Ingeneral, the halides are combined with the catalyst by contacting asuitable compound, such as, hydrogen fluoride, ammonium fluoride,hydrogen chloride, ammonium chloride, either in the gaseous form or in awater soluble form with the catalyst. Preferably, the fluoride orchloride is incorporated with the catalyst from an aqueous solutioncontaining the halide.

Typically, the isomerate stream is passed to a separation system wherebythe isomerate stream is separated into a recycle hydrogen stream, astream of light hydrocarbons and hydrogen, a stream comprising thedesirable isomer, and a recycle stream comprising the unconverted normalparaffin. Additionally, a heavy recycle stream, comprising compoundshaving relative volatilities lower than that of the unconverted normalparaffin in the recycle stream, can also be provided for by theseparation means.

A common arrangement for the separation system is to feed the isomeratestream to product separator means in which a gas phase and a liquidphase are separated. The gas phase comprises primarily hydrogen, whichis recycled to be mixed with the reactor feed stream and, preferably,with a combined reactor feed and recycle stream prior to charging thethus formed mixture to the isomerization reactor. As for the liquidphase from product separator means, it is generally charged tostabilizer separation means whereby the lighter hydrocarbons and theremaining hydrogen that is dissolved in the liquid is separated from ahydrocarbon mixture comprising the desired alkane isomer, theunconverted normal alkane, and the heavy recycle stream compounds. Thishydrocarbon mixture is then fed to fractionator separation means wherebya split between the desired isomer and a mixture of the unconvertednormal paraffin and heavy recycle stream compounds is made. Generally,an overhead stream from fractionator separation means contains thedesired isomer and a bottoms stream will contain essentially thosecompounds having a relative volatility lower than that of the desiredisomer. A preferred embodiment of the invention will provide a medialstream or sidedraw stream used as the recycle stream comprisingprimarily the unconverted normal paraffin, and the bottoms stream isused as the heavy recycle stream.

The preferred embodiment of the invention is to provide the separationsystem to separate the isomerate stream into at least a third stream, afourth stream and a fifth stream. The fourth stream, which comprisesprimarily the unconverted normal alkane feed to the isomerizationreactor, can preferably be recycled to be mixed with the reactor feedstream prior to charging the thus formed mixture to the isomerizationreactor. As an optional feature of this invention, the fourth stream ora portion of such stream may be fed to storage. The fifth streamcomprises primarily at least a portion of the heavy compounds of theisomerate stream, which have relative volatilities lower than that ofthe unconverted normal paraffin compounds. The fifth stream ispreferably recycled and mixed with the hydrocarbon feed mixture prior tothe thus formed mixture undergoing the earlier mentioned separation stepwhereby the heavy compounds are removed along with the earlier describedheavier hydrocarbons. At least a portion of the fifth stream can beutilized, either on a continuous basis or an intermittent basis, toregenerate the earlier described adsorbent when it is spent.

Because it is frequently necessary to regenerate the adsorbent material,a feature of this invention includes the use of at least a portion ofthe fifth stream as a purge stream to regenerate the adsorbent material.It is generally necessary to regenerate the adsorbent material on acyclic basis with the regeneration cycle times ranging upwardly to asoften as every 24 hours or longer. The regeneration of the adsorbentmaterial is accomplished by purging at elevated temperatures with atleast a portion of the fifth stream. Preferably, the regeneration isaccomplished by passing the heated at least a portion of said fifthstream through the bed of adsorbent material. The purging is generallyperformed until a very limited amount of water and sulfur compounds areevident in the exiting regeneration purge stream. Suitably, regenerationis conducted at a temperature of from about 200° F. to about 600° F. Inorder to maintain frequent regeneration of the adsorbent material, itcan be desirable to have several parallel adsorbent beds so that as oneis removed for regeneration others may be used for adsorption; thus, acontinuous process can be maintained.

The regeneration purge stream can be mixed with the incoming hydrocarbonfeed mixture in the same manner as is the fifth stream.

Referring now to FIG. 1, there is provided a schematic representation ofa hydrocarbon treating system 10 for a preferred embodiment of theinvention. Conduit 12 shown provides for fluid flow to a medial sectionof depentanizer fractionator column or depentanizer 14 which has anoverhead outlet 16 and a bottoms outlet 18. Conduit 20 is operablyconnected with bottoms outlet 18 for conveying fluid from depentanizer14. Providing for fluid flow communication between overhead outlet 16and bottom inlet 22 of countercurrent extractor 24 is conduit 26 whichis operably connected between overhead outlet 16 and bottom inlet 22 forconveying fluid from depentanizer 14 to countercurrent extractor 24.Interposed in conduit 26 are heat exchanger 28, having an inlet 30 andan outlet 32, and heat exchanger 34.

Countercurrent extractor 24 is additionally provided with a top inlet36, an overhead outlet 38 and a bottoms outlet 40. Conduit 42 isoperably connected between overhead outlet 38 and inlet 30 to providefor fluid flow communication from countercurrent extractor 24 to heatexchanger 28. Conduit 44 is operably connected between outlet 32 andinlet 46 of pentane fractionator column or pentane splitter 48 toprovide for fluid flow communication from heat exchanger 28 to pentanesplitter 48. Pentane splitter 48 is additionally provided with anoverhead outlet 50 and a bottoms outlet 52. Conduit 54 is operablyconnected to overhead outlet 50 for conveying fluid from pentanesplitter 48.

Providing for fluid flow communication between bottoms outlet 52 and theinlet to valves 56 and 58 is conduit 60. Conduit 62 provides for fluidflow communication between the outlet of valve 56 and dryer vessel 64and conduit 66 provides for fluid flow communication between the outletof valve 58 and dryer vessel 68. Conduit 70 provides for fluid flowcommunication between dryer vessel 64 and the inlet of valve 72, andconduit 74 provides for fluid flow communication between dryer vessel 68and the inlet of valve 76. Fluid flow communication between the outletsof valves 72 and 76 and isomerization reactor vessel 78, which has aninlet 80 and an outlet 82, is provided for by conduit 84 that isoperably connected between valves 72 and 76 and inlet 80. Fluid can beconveyed from dryer vessels 64 and 68 to isomerization reactor vessel 78via conduit 84. Operably connected to conduit 84 is conduit 85 whichprovides for fluid flow to conduit 84.

For separating a fluid into five separate fluid streams is separationsystem 86 having an inlet 88, a first outlet 90, a second outlet 92, athird outlet 94, a fourth outlet 96 and a fifth outlet 98. Conduit 100is operably connected between outlet 82 and inlet 88 for conveying fluidfrom isomerization reactor vessel 78 to separation system 86. Forconveying fluid from separation system 86 to conduit 84 is conduit 102which is operably connected between first outlet 90 and conduit 84.Conduits 104 and 106 are operably connected to second outlet 92 andthird outlet 94, respectively, for conveying fluid from separator system86. For conveying fluid from separation system 86 to conduit 84 isconduit 108 which is operably connected between fifth outlet 98 andconduit 84.

For recycling fluid from separator system 86, conduit 110 is provided.Conduit 110 is operably connected between fourth outlet 96 and conduit12 and inlet 112 of heat exchanger 114 for conveying fluid fromseparator system 86 to either heat exchanger 114 or conduit 12, or both.Heat exchanger 114 is also equipped with outlet 116. Providing for fluidflow communication between outlet 116 and the inlets of valves 118 and120 is conduit 122 which is operably connected between outlet 116 andthe inlet of valves 118 and 120. Conduits 124 and 126 are respectivelyconnected with the outlets of valves 118 and 120. For conveying fluidfrom valves 118 and 120 to dryer vessels 64 and 68, respectively,conduit 124 is operably connected between the outlet of valve 118 andconduit 70 and conduit 126 is operably connected between the outlet ofvalve 120 and conduit 74.

For removing fluid from dryer vessels 64 and 68 are conduits 128 and130. Conduit 128 is operably connected between conduit 62 and the inletof valve 132 for conveying fluid from dryer vessel 64 to valve 132.Conduit 130 is operably connected between conduit 66 and the inlet ofvalve 134 for conveying fluid from dryer vessel 68 to valve 134. Forconveying fluid from the outlets of valves 132 and 134 to inlet 136 ofheat exchanger 138 is conduit 140 which is operably connected betweenthe outlets of valves 132 and 134 and inlet 136. Heat exchanger 138 isadditionally provided with outlet 142.

For conveying fluid from heat exchanger 138 to separation vessel 144 isconduit 146. Separation vessel 144 is equipped with a top inlet 148, atop outlet 150 and a bottom outlet 152. Conduit 146 is operablyconnected between outlet 142 and top inlet 148 for conveying fluid fromheat exchanger 138 to separation vessel 144. Operably connected tobottom outlet 152 is conduit 154 for conveying fluid from separationvessel 144. Providing for fluid flow communication between conduit 12and separation vessel 144 is conduit 156 which is operably connectedbetween top outlet 150 and conduit 12.

Conduit 158 is operably connected between bottoms outlet 40 and inlet160 of heat exchanger 162 for conveying fluid from countercurrentextractor 24 to heat exchanger 162 which is provided with an inlet 160and an outlet 164. Conduit 166 is operably connected to conduit 158 toprovide for fluid flow to conduit 158. Operably connected between outlet164 and bottom inlet 168 of oxygenation reactor 170 is conduit 172.Oxygenation reactor 170 is provided with bottom inlet 168 and overheadoutlet 174 for allowing fluid flow through oxygenation reactor 170.

Fluid flow communication between settler separator 176, having an inlet178, an overhead outlet 180, and a bottoms outlet 182, is provided forby conduit 184 which is operably connected between overhead outlet 174and inlet 178. Conduit 186 is operably connected to overhead outlet 180for conveying fluid from settler separator 176. Conduit 188 is connectedbetween bottoms outlet 182 and top inlet 36 for conveying fluid fromsettler separator 176 and countercurrent extractor 24. Interposed inconduit 188 is pump 190 for imparting energy head to the fluid passingthrough conduit 188.

In operating hydrocarbon treating system 10, a hydrocarbon feed mixtureis charged to hydrocarbon treating system 10 through conduit 12. It ispreferred that the hydrocarbon feed mixture comprise primarilyhydrocarbons having at least 5 carbon atoms. The hydrocarbon feedmixture is charged to depentanizer 14 which defines a separation zoneand provides means for separating the hydrocarbon feed mixture. Indepentanizer 14, the hydrocarbon feed mixture will be separated into twostreams, one comprising primarily pentane and lighter compounds, whichis the overhead of depentanizer 14 that passes through conduit 26, andthe bottoms product stream, which comprises primarily cyclopentane andheavier compounds, that passes by way of conduit 20 to storage or tofurther downstream processing.

The pentane and lighter hydrocarbons pass by way of conduit 26 tocountercurrent extractor 24 which defines a contacting zone and providesmeans for caustic treating the pentane and ligher hydrocarbons.Optionally, the pentane and lighter stream can exchange heat withcertain heat transfer mediums by use of heat exchangers 28 and 34 whichprovide means for the indirect exchange of heat between the pentane andlighter stream and heat transfer mediums. Within countercurrentextractor 24, the pentane and lighter hydrocarbons are contacted in acountercurrent fashion with a caustic composition such as an alkalinesolution. In the presently preferred case where the alkaline solution issodium hydroxide in an aqueous phase, most of the mercaptan compoundscontained within the hydrocarbon stream will be removed in the form ofwater and RSNa, where R is an alkyl group. The thus caustic-treatedhydrocarbons will pass by way of conduit 44 to pentane splitter 48 whichprovides means for separating the caustic-treated hydrocarbons into anoverhead stream comprising primarily isopentane and a bottoms streamcomprising primarily normal pentane. Optionally, the caustic-treatedhydrocarbon mixture can pass through heat exchanger 28 to exchange heatwith the pentane and lighter hydrocarbons being charged tocountercurrent extractor 24 via conduit 26.

The contacted alkaline solution exits countercurrent extractor 24through conduit 158 to oxygenation reactor 170. Within oxygenationreactor 170, the mercaptans contained within the alkaline solution areconverted into insoluble organic disulfide compounds by reacting thecompounds with an oxygen-containing gas, such as air. Air is injectedinto the solution via conduit 166. The thus formed organic disulfidesand aqueous solution pass by way of conduit 184 to settler separator176, which defines a separation zone and provides means for separatingat least a substantial portion of the organic disulfides and otherorganic sulfur compounds from the alkaline solution. The thus separatedalkaline solution, having a significant reduction in the concentrationof organic disulfides and organic sulfur compounds, is recycled throughconduit 188 to countercurrent extractor 24 wherein it is used as thealkaline solution for contacting with the pentane and lighterhydrocarbons entering countercurrent extractor 24 via conduit 26.

Pentane splitter 28 defines a separation zone and provides means forseparating the caustic-treated hydrocarbons into an overhead stream anda bottoms product stream. Preferably, the overhead stream comprisesprimarily isopentane and lighter compounds that pass by way of conduit54 to either storage or for further downstream processing. The bottomsproduct stream comprises primarily normal pentane and heavierhydrocarbon compounds, water and sulfur compounds, which includedisulfides, that can be present in the caustic-treated hydrocarbon feedmixture. The normal pentane and heavier hydrocarbon stream, laden withthe water and sulfur compounds, passes by way of conduit 60, valve 58and conduit 66 to dryer vessel 68. Alternatively, the normal pentane andheavier hydrocarbon stream can pass by way of conduit 60, valve 56 andconduit 62 to dryer vessel 64. The desired fluid flow direction can becontrolled by maintaining either valve 56 or valve 58 in the closedposition. Dryer vessels 64 and 68 define a contacting zone and providemeans for contacting the normal pentane and heavier hydrocarbon streamwith an adsorbent material to remove water and sulfur compounds from thenormal pentane and heavier hydrocarbon stream and produce a reactor feedstream. The preferred adsorbent material contained within dryer vessels64 and 68 is the molecular sieve adsorbent material previously describedherein.

The desired fluid flow through either dryer vessel 64 or dryer vessel 68is controlled by maintaining either valve 72 or valve 76, in cooperationwith valves 56 and 58, in a closed position. Following is an example toillustrate the operation of dryer vessel 64 and 68. If it is desired topass the bottoms product stream of pentane splitter 48 through dryervessel 68, valves 56 and 72 are kept in the closed position to block theflow of pentane splitter 48 bottoms product stream through dryer vessel64. Valves 58 and 76, on the other hand, are maintained in the openposition to permit the flow of pentane splitter 48 bottoms productstream through dryer vessel 68. Alternatively, if it is desired to passthe bottoms product stream of pentane splitter 48 through dryer vessel64, valves 58 and 76 are kept in the closed position to block fluid flowthrough dryer vessel 68 and valves 56 and 72 are maintained in the openposition to permit fluid flow through dryer vessel 64.

The reactor feed stream from either dryer vessel 64 or dryer vessel 68passes by way of conduit 84 to isomerization reactor 78 wherein it iscontacted with an isomerization catalyst, as earlier described herein,contained within isomerization reactor vessel 78 to produce an isomeratestream or isomerization reactor effluent. Isomerization reactor vessel78 defines a reaction zone and provides means for isomerizing thereactor feed stream from either dryer vessel 64 or dryer vessel 68 or,alternatively, contacting the reactor feed stream with the isomerizationcatalyst. The isomerate stream passes by way of conduit 100 toseparation system 86 which defines a separation zone and provides forseparating the isomerate stream into at least four separate streams but,preferably, into at least five separate streams. In separation system86, the isomerate stream is separated into a stream comprising butaneand lighter hydrocarbons that passes from separator system 86 by way ofconduit 104 for downstream processing or use, a stream comprisingprimarily isopentane that passes from separator system 86 by way ofconduit 106 for downstream use or storage, a recycle stream comprisingprimarily normal pentane that passes from separator system 86 by way ofconduit 108 to be mixed with the reactor feed stream flowing throughconduit 84 prior to charging the mixture to isomerization reactor vessel78, a recycle hydrogen stream that passes from separator system 86 byway of conduit 102 to be mixed with the reactor feed stream flowingthrough conduit 84 and make-up hydrocarbon introduced by way of conduit85 prior to the feeding the thus formed mixture to isomerization reactorvessel 86, and a heavy recycle stream comprising cyclopentane andheavier components that is recycled from separation system 86 viaconduit 110.

At least a portion of the heavy recycle stream passing through conduit110 can be recycled to conduit 12 to be mixed with the incominghydrocarbon feed mixture prior to feeding the thus formed mixture todepentanizer 14. Additionally, at least a portion of the heavy recyclestream passing from separation system 86 by way of conduit 110 can beutilized as a purge stream to regenerate the adsorbent materialcontained within dryer vessels 64 and 68. Heat exchanger 114 is used toprovide heat exchange means for heating the regeneration purge streamprior to feeding it to either dryer vessel 64 or dryer vessel 68 toregenerate the molecular sieve material contained within the vessels. Inoperating dryer vessels 64 and 68, preferably, one dryer vessel will beundergoing a regeneration cycle while the other vessel is simultaneouslyundergoing a contacting or adsorption cycle. For example, if dryervessel 64 is undergoing a regeneration cycle and dryer vessel 68 isundergoing a contacting cycle, valves 58, 76, 118, and 132 will be inthe open position and valves 56, 72, 120 and 134 will be in the closedposition. These valve positions will result in directing the purgestream through dryer vessel 64 to regenerate the molecular sievematerial contained in dryer vessel 64, and the valve positions willresult in directing the bottoms stream from pentane splitter 48 throughdryer vessel 68 to be contacted with the molecular sieve materialcontained therein. To alternate the fluid flows, the valve positions arereversed thus completing a regeneration-contacting cycle.

The hot purge stream passing through the adsorbent materials withineither dryer vessel 64 or dryer vessel 68, passes as a regenerativeeffluent stream by way of conduit 140 to a separation vessel 144 whichdefines a separation zone and provides separation means whereby thewater that is removed from the adsorbent material is separated from thehydrocarbon that is in said regeneration effluent stream. Heat exchanger138 provides heat exchange means for removing heat from the regenerationeffluent stream in order to condense the hydrocarbon and water streampassing through conduit 140. The water separated in separation vessel144 passes by way of conduit 154 to downstream disposal and theseparated hydrocarbon from separation vessel 144 passes by way ofconduit 156 to conduit 12 wherein it is mixed with the incominghydrocarbon feed mixture to form a hydrocarbon feedstream which ischarged to depentanizer 14. The sulfur compounds and the remainingunremoved water purged from the adsorbent materials contained in dryervessels 64 and 68 are ultimately removed with the bottoms product streamof depentanizer 14 via conduit 20.

The hereindescribed invention provides for the efficient removal ofcontaminating quantities of water and sulfur compounds fromhydrocarbon-containing streams. Because of the resultant reduced levelsof contaminating sulfur compounds and water in the isomerizationreaction zone feed, a significant improvement in the conversion ofstraight chain hydrocarbons to their corresponding branched chainisomers can be achieved. By utilizing the method and apparatusdescribed, a high purity isopentane product suitable for use in theproduction of linear low density polyethylene can be economicallyproduced.

While the invention has been described in terms of the presentlypreferred embodiment, reasonable variations and modifications arepossible by those skilled in the art. Such variations and modificationsare within the scope of the described invention and the appended claims.

That which is claimed is:
 1. Apparatus for treating a caustic-treatedhydrocarbon feed mixture having a contaminating concentration of waterand sulfur compounds, comprising:first separating means for separating acaustic-treated hydrocarbon feed mixture into a first stream comprisingnormal pentane and heavier hydrocarbon compounds and a second streamcomprising isopentane and lighter hydrocarbon compounds; firstcontacting means for contacting said first stream with a molecular sievematerial to adsorb water and sulfur compounds from said first stream andto thereby produce a reactor feed stream having a significant reductionin the concentration of said water and sulfur compounds; first conduitmeans operably connected between said first separating means and saidfirst contacting means for conveying said first stream to said firstcontacting means; isomerizing means for isomerizing said reactor feedstream by contacting said reactor feed stream in the presence ofhydrogen under suitable isomerization conditions with an isomerizationcatalyst to produce an isomerate stream comprising isopentane, normalpentane, butane and lighter hydrocarbons, and cyclopentane and heavierhydrocarbons; second conduit means operably connected between said firstcontacting means and said isomerizing means for conveying said reactorfeed stream to said isomerizing means; second separating means forseparating said isomerate stream into at least a heavy recycle streamcomprising cyclopentane and heavier hydrocarbons, a light hydrocarbonsand hydrogen stream comprising butanes and lighter hydrocarbons, arecycle stream comprising normal pentane, and an isopentane streamcomprising isopentane; third conduit means operably connected betweensaid isomerizing means and said second separating means for conveyingsaid isomerate stream to said second separating means; second contactingmeans for contacting said first stream with said molecular sievematerial to adsorb water and sulfur compounds from said first stream andto thereby produce said reactor feed stream having a significantreduction in the concentration of said water and sulfur compounds;fourth conduit means operably connected between said second contactingmeans and said second separating means for conveying said heavy recyclestream from said second separating means to said second contactingmeans; third separating means for separating water from saidregeneration effluent stream to produce a dewatered effluent stream;fifth conduit means operably connected between said second contactingmeans and said third separating means for conveying said regenerationeffluent stream from said second contacting means to said thirdseparating means; fourth separating means for separating a mixedhydrocarbon feed stream into an overhead stream and a bottoms productstream; sixth conduit means for conveying said dewatered effluent streamto a seventh conduit, said sixth conduit means is operably connectedbetween said third separating means and said seventh conduit meanswhereby said dewatered effluent stream is mixed with a hydrocarbon feedmixture having a contaminating concentration of sulfur compounds toproduce said mixed hydrocarbon feed stream and wherein said seventhconduit means is operably connected to a medial portion of said fourthseparating means for conveying said mixed hydrocarbon feed stream tosaid fourth separating means; third contacting means for contacting saidoverhead stream with a caustic composition to remove sulfur compounds tothereby produce said caustic-treated hydrocarbon feed mixture; eighthconduit means operably connected between said fourth separating meansand said third contacting means for conveying said overhead stream fromsaid fourth separating means to said third contacting means; and ninthconduit means operably connected between said third contacting means andsaid first separating means for conveying said caustic-treatedhydrocarbon feed from said third contacting means to said firstseparating means.
 2. Apparatus as recited in claim 1, furthercomprising:a first valve interposed in said first conduit means, asecond valve interposed in said second conduit means, a third valveinterposed in said fourth conduit means, a fourth valve interposed insaid fifth conduit means, tenth conduit means, wherein interposed is afifth valve, operably connected to said first conduit means at aposition between said first separating means and said first valve andoperably connected to said fifth conduit means at a position betweensaid second contacting means and said fourth valve for providing fluidflow communication between said first conduit means and said fourthconduit means; eleventh conduit means, wherein interposed is a sixthvalve, operably connected to said fifth conduit means at a positionbetween said third separating means and said fourth valve and operablyconnected to said first conduit means at a position between said firstcontacting means and said first valve for providing fluid flowcommunication between said first conduit means and said fifth conduitmeans; twelfth conduit means, wherein interposed is a seventh valve,operably connected to said second conduit means at a position betweensaid first contacting means and said second valve and operably connectedto said fourth conduit means at a position between said third valve andsaid second separating means for providing fluid flow communicationbetween said second conduit means and said fourth conduit means; andthirteenth conduit means, wherein interposed is an eighth valve,operably connected to said fourth conduit means at a position betweensaid second contacting means and said third valve and operably connectedto said second conduit means at a position between said second valve andsaid isomerization means for providing fluid flow communication betweensaid fourth conduit means and said second conduit means.